event-manager: remove the auto-remove timer when the event is destroyed
event-manager: remove the auto-remove timer when the event is destroyed

This avoid to crash when trying to re-remove an old event (#603485).

GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets